EMPLOYEE BENEFITS - Schedule of Long-term Rates of Return on Pension and PBOP (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
United States
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	21.50%	22.00%
Assumed Rate of Return	8.50%	8.50%
International
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	11.00%	13.00%
Assumed Rate of Return	8.50%	8.50%
Emerging Markets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.50%	5.00%
Assumed Rate of Return	10.00%	10.00%
Private Equity
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	12.00%
Assumed Rate of Return	12.00%	12.00%
Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	11.00%	12.00%
Assumed Rate of Return	4.00%	4.50%
Public High Yield Fixed Income
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	3.00%
Assumed Rate of Return	6.50%	7.00%
Private Debt
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	15.00%	10.00%
Assumed Rate of Return	9.00%	9.00%
Emerging Markets Debt
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	2.00%	5.00%
Assumed Rate of Return	6.50%	7.50%
Real Estate and Other Assets
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	12.00%	10.00%
Assumed Rate of Return	7.50%	7.50%
Hedge Funds
Defined Contribution Plan Disclosure [Line Items]
Target Asset Allocation	4.00%	8.00%
Assumed Rate of Return	6.00%	7.00%